Ultrasonic transducers having a structure shown in FIG. 4 are hitherto disclosed, as the ultrasonic transducers used in ultrasonic flow meters of a certain kind (refer to Patent Literature 1, for example).
Description is provided hereinafter about a structure of a conventional ultrasonic transducer by referring to FIG. 4. FIG. 4 is a schematic drawing showing the conventional ultrasonic transducer in a position mounted on a flow channel.
As shown in FIG. 4, conventional ultrasonic transducer 68 includes closed-top cylindrical case 63, piezoelectric element 64, and retainer 66 formed from vibration damper 65 and vibration conduction suppressor 67 in a single-piece structure. Case 63 has top portion 60, sidewall 61, and support portion 62 extending outward from sidewall 61. Piezoelectric element 64 is fixed to an inner wall face of top portion 60 of case 63. Vibration damper 65 is so disposed as to cover and stay in close contact with an outer periphery of sidewall 61 of case 63, to suppress vibrations of sidewall 61 attributed to vibrations of piezoelectric element 64. Retainer 66 retains support portion 62 of case 63. Vibration conduction suppressor 67 of retainer 66 is generally formed of a flexible material having high damping properties, and it holds case 63 in vibration free to mounting portion 69a of flow channel 69. Ultrasonic transducer 68 is fixed to flow channel 69 with screw 71, while being held pressed against vibration conduction suppressor 67 of retainer 66 via sensor holder 70. With this structure, ultrasonic transducer 68 measures a flow rate of the fluid.
In a case that the ultrasonic transducer of the above structure is used for an ultrasonic flow meter, vibration conduction suppressor 67 of retainer 66 and ultrasonic transducer 68 are made up from separate parts. It is therefore necessary that vibration conduction suppressor 67 is attached into tight contact with ultrasonic transducer 68. There has been a problem of mass-productivity, however, that it requires a certain time for adjustment when vibration conduction suppressor 67 of pliable nature is attached uniformly to ultrasonic transducer 68.
There is also a case in which vibration conduction suppressor 67 does not adequately serve its intended function due to a variation in mounting accuracy of vibration conduction suppressor 67. Reverberant noise and vibrations that become noises in the measurement are therefore transmitted to flow channel 69 during the flow measurement. As a result, it gives rise to a drawback in which the noises conducted through the case increases, and measuring accuracy of the flow rate of the fluid decreases.
In addition, there is another case in which tightening torque of screw 71 is prone to vary when ultrasonic transducer 68 is mounted on flow channel 69 via sensor holder 70. This results in conduction of the vibrations of ultrasonic transducer 68 to flow channel 69. There is hence a possibility of increasing the conduction noises through the case, and decreasing the measuring accuracy of the flow rate of the fluid.